Transmission-dynamometer.



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Patented N ov. 17, 1908.

2 SHEETS-SHEET 1.

B. HOPKINSON n L. G. P. THRING.

TRANSMISSION DYNAMOMBTER.

APPLICATION FILED JUNE 11, 1907.

Patented Nov. 17, 1908.

3 SHEETS-SHEET 3.

49 .Mum/m2@ B. HOPKINSON & L. G. P. THRING. TRANSMISSION DYNAMOMETER.

APPLICATION FILED JUNE 11, 1907.

904,432. Patented Nov. 17, 190s.

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BERTRAM HPKIN SON AN D LEONARD GODFREY PIN N EY THRIN G, OF CAMBRIDGE,ENGLAND.

TRAnsMissIoN-DYNAMOMETER.

Specification of Letters Patent.

Patented Nov. 17, 1908.v

Application led June 11, 1907. Serial No. 878,328. I

To all whom 'it may concern:

Be it known that we, BERTRAM HOPKIN- soN and LEONARD GoDrREY PINNEYTHRiNG, both subjects of the King of GreatBritain, residing,respectively, at the Engineering Laboratory, Cambridge, andl/Valsingham, Millington Road, Cambridge, both in lthe county ofCambridge, England, have invented certain new and useful Improvements inTransmissionDynamometers, of

which the following is a specification.

This invention relates to transmission dynamoineters the chief objectbeing to enable the power transmitted byV a rotating shaft to beaccurately determined by measuring the angle of twist of the shaftbetween two points thereon at a definite distance apart while the shaftis rotating.

(')ne feature of this invention consists in the employment of meanswhereby the small amount of twist undergone by 'the shaft is renderedvisible, so that the amount thereof at any moment can be observed andmeasured. L

A further feature of the invention consists in means whereby errors dueto friction, vibration and the like are detected or eliminated. It willbe understood that, since the angle of twist to be measured is verysmall, the means for eliminating the .said errors forni an importantpart of the invention.

For the purpose of this invention the rotating shaft, by which the powerto be determined is transmitted, is provided with two members, which areattached to the said shaft at a definite distance apart and are providedwith a mirror so mounted in relation to the aforesaid members that therelative angular displacement of the latter, due

to the twist of the shaft between their points of attachment, isaccurately imparted to the mirror. The movement of the mirror isrendered visible by allowing a beaml of light to fall thereon and to bereflected to a suitable point of observation by the same.

In order that the fsaid invention may be clearly understood and readilycarried into effect, we will proceed to describe the same more fullywith reference tothe accompanying drawings in which Figure -1 is a sideelevation and Fig.V 2 a plan of one arrangement embodying the mainfeatures of our invention. Figs. 3 and 4t are cross sections on thelines 1-1 and 2`2 of Fig. 1. Figs. 5 and 6 are respectively an elevationand plan of a scale employed with the source of light. Figs. 7 and 8 arerespectively an enlarged front and side elevation of the 'mirror andmounting illustrated in Figs. l and 2. Fig. 8 shows a modifiedarrangement of the mirror-actuating means. Fig. 9 is a plan and Fig. 10an end View of a modified construction of vattachment between the twomembers comprising the'dynamometer. Figs 1l, 12 and 13 are respectivelyan end elevation, crosssection, and plan of a further modifiedconstruction of our invention. Figs. 11a and ll" are a cross sectionalelevation and side elevation respectively showing certain moditieddetails, and Fig. 1lc is'a sectional elevation similar to Fig. 11 buttaken from the left of Fig. l2 and showing a modified arrangementforsupporting the free end of the' sleeve; Figs. 14, 15 and 16 are detailviews of the mirror and its mounting employed with the modifiedconstruction shown in Figs. 1l to 13. Fig. 17 is a detail sectional viewof a portion of the bearing shown in Fig. 11.

A is the shaft, and B, C, are the two members attached thereto.

D is the mirror, whereof the'rays reiiected by the mirror indicate themovement of the same.

Referring more particularl to Figs. l and 2, the member B, hereina ercalled the sleeve, is clamped to the shaft A by radial screws B or theirequivalents. The other member C, hereinafter called the collar, is

clamped in a similar manner by the screws and E the source of light CIKC. ln the simplest construction, the sleeve and collar might` be rigidlysecured to the shaftquite independently ofeach other thus engaging onlythrough the intervention of the mirror; but as the attachment of thesemembers to the shaft merely by three or more screws would not usually besufficiently rigid to obtain accurate results in practice, particularlyif the sleeve is long in proportion to its diameter, we have shown inthe figures now referred to a construction in which the attachment ofthe aforesaid members is reinforced by sliding bearings C2 which connectthe sleeveand collar together so as to permit only of rotational motionabout the axis of the shaft, the sleeveB being arranged 'to iit'accurately within the inner end of the collar C. The respectiveattachments of the-sleeve and collar to the shaft at the points betweenwhich the twist is to be measured must not in this case be ico the armabsolutely rigid but must permit small angular `motions about an axisperpendicular to the axis of the sha ft such as are necessary toaccommodate the motion of the sleeve to that of the collar withoutstraining the bearing between them. The mirror D 1s mounted on a spindleD, the latter being carried by the collar C and provided with a shortarm D2 which engages with an armI oractuating plate B2 on the sleeve Bso that any relative 'angular motion of the sleeve and collar causes themirror to become an larly displaced about the axis of its spind e D. Theshort arm D2 is shown provlded at its free end with a smoothanti-friction ball D8 for engagement with the face of the actuatingplate B2, although it will be understood that the ball might be placedon the actuating plate B2 in which case the short arm D3 would terminatein a flat plate `as shown in Fig. 8a. The ball D3 is kept in contactwith the actuating plate by the sprin D4 which is1 here shownsecured tothe sai actuating p ate.

It will be understood that we do not of course desire ,to limitourselves to the ball and its actuating plate arrangement for impartingmotion to the mirror as any other evice adapted to perform thisoperation in a. practically frictionless manner will answer our purpose.v

In order that any relative motion of the sleeve and collar may causeangular motion of the mirror it is necessary that the bearing surface ofthe actuating plate B2 be inclined to a line p erpendicular to thespindle D and 2. In Figs. l and 2 the angle between these directions isa right angle. The

- effect of varying this angle is to vary the amount by which the mirroris moved for the same angular movement of the actuating late. The saidactuating plate must also `e inclined to the direction normal to theaxis of the shaft, and ythe line joining the point of contact of theball and the actuating plate to this axis.

The amount by which the mirror D is turned is proportional to therelative angular motion of the sleeve and collar and consequently to theangle of torsion of the shaft between their points of attachment. Theaxis of the mirror D is so disposed relatively to the axis of the shaftA that when a beam of light coming from the source of light E isreflected from said mirror and is received in the field of a telescopeF, angular motion of the mirror about its spindle Dl causes therefiected beam to traverse the field of the telescope. The beam of lightemerging from the source E, which may conveniently be the filament of anelectric lamp, is reflected onto the field of the telescope F once inevery revolution of the shaft, so that said image appears as a brightline of light crossing the field of vision. The telescope F is .providedwith cross wires so as to permit displacement imparted to the mirror,owing to the torsion of the shaft when transmitting power, causes theline of light in the field of vision of the telescope to move laterally,and the image is brought back again to the center of the field of visionof the telescope by adjusting the position of the source of light Ealong the scale E on which said source of light is mounted to slide. Theamount by whlch the source of light is moved along the scale serves as ameasure of the angular displacement of the mirror, and consequently ofthe twist undergone by the shaft A between the points of attachi-ment ofthe sleeve B and collar C. It may yhere be stated that the slidingbearings between the sleeve and the collar or between these members andthe shaft in such a manner as to permit relative motion of the sleeveand collar other than a pure rotation as friction between the parts canthen be more easily eliminated. We therefore, in some forms of ourinvention, make use of the fact that relative motion between sleeve andcollarl will not produce any delection of the mirror and therefore willcause no error in the reading provided that it is of such a character asto cause the ball to move parallel to the plane of the actuating plate.The same principle is applied in dealing with the mutual displacementsof sleeve and collar which may arise from the bending of the shaft; theactuating plate being 1alaced in such a position and with such aninclination that t-hese displacements cause motion in the plane of theactuating plate only. l

The above stated principles are applied to the constructions illustratedin Figs. 9 to 17. Referring to Figs. 9 and 10, the sleeve B and thecollar C are secured to the shaft at the points between which the twistis to be measured by the screws B" and C. Bearings between the saidsleeve and collar are afforded by the set screws C3 and the rollers C,one of which may be controlled by a spring C5. The collar is showncarrying two mirrors although it will be understood that only one needbe employed. The ball D3 on the end of the arm D2 of each mirror D ispressedv upon by an actuating plate B2 of the sleeve B, and from aconsideration of the shaft are not communicated to the mirlarly flangedat the end B3 which is adjacent to the collar. One member carries themirror D and the other` carries the projecting plate `or mirroractuatingarm B2. As shown, it is the collar which carries the mirror. The collarC is provided with three bosses CT which project through'apertures inthe extended portion B4 ofthe sleeve B, the said bosses CT permittingthree radial screws to engage with the shaft and thus secure the collarthereto.

Connection between thev sleeve B and collar C is afforded by the twosimple screws G and the resilient bearing G2, the latter having aplunger controlled by a spring G3 (Fig. 17) vand adapted to slide withinthe central guide G4, which is free to make small oscillations about itsbase at G5.

In 'place of the rollers C4' shown in Fig. 10, or of the rounded screwsG1 shown in Fig. 11, we may employ short columns GX as shown in Figs.11*l and 11b, these columns having curved ends shaped to a definite andpredetermined radius, the said ends being suitably constrained so thattheir movement on the collar or sleeve causes rolling friction asdistinguished from sliding friction.

Instead of a sliding bearing between the collar C and the free end ofthe sleeve B as shown in Fig. 1, or instead of the connection shown in F11 between these parts, the free end of the sleeve may be supporteddirectly upon the shaft as shown in Fig. 11C, where the two simplerounded screws Gr1 and the resilient bearini'gr G2, similar to thoseshown in Fig. 11, connect the said sleeve directly to the shaft, theconnection being functionally as in the other arrangements,

that is to say, such that angular motion of this end ofthe sleeve is notrestrained. rIhe flanges of the sleeve and collar are yieldingly. heldtogether by steady springs C8.

rl`he mirror D is carried by a frame D5 which is secured to the face ofthe fiange C of the collar C by a screw bolt C". The extremities of thespindle D on which the mirror is fixed are mounted between the lugs D ofthe frame D5. One of the said 'extremities bears upon a resilient plateor flat spring D7, the opposite end being pressed upon by a set screwDs. The actuating plate B2 is secured to the flange B3 of the sleeveI Band operates against the spring D4 which bears upon the ball D3. bestated that an advantage of employing large flanges C, B3, is that themotion imparted to the mirror increases as its distance from the axis ofthe shaft increases, this arrangement being equivalent to-increasing thedistance between the oints of attachment of sleeve and collar to t eshaft. In this construction it will be seen that the principleshereinbefore mentioned are again involved owing to the fact that theaxis of the mirror is arranged so as to lie in the plane of attachmentof the collar to the shaft, and the plane of contact between the balland plate is arranged so as to be parallel to the axis of the shaft.

Errors in reading, due to angular displacement of the sleeve and collarabout axes at right angles to the shaft may be detected and allowed forby observing the reflections in mirrors fixed to these members, of asource of light if it is desired to dispense with the above describedmethodsl of construction for eliminating these errors.- Similarly,bending or deflection of the shaft between the points of attachment ofthe sleeve and collar may arise from deflection occurring in the shaftat points beyond the length ofshaft under consideration and thus causeerror which though generally negligible may be similarly allowed for, ifnecessary, by fixing a mirror such as B", Figs. 11a and 11b, rigidly tothe sleeve B and adjusting the source of light E and telescope F so thatthe reflection of the light appears in the center of the field of thetelescope when the shaft is at rest, and then observing the displacementof the image produced when the shaft revolves.

Although we have described the invention as carried into effect by theuse of a telescope, the latter is not absolutely necessary. In place ofthe plane mirror D, a concave mirror may, for example be employed so asto focus the beam of light on to a semitransparent scale which ittraverses by an amount proportional to the angle of twist of the shaft.

As details of construction it may be mentioned that the position of themirror and its actuating plate may be interchanged if necessary; alsothat the various points of contact between different parts may ifdesired be surrounded by leather washers or the like to prevent accessof dust.

What we claim and rdesire to secure by Letters Patent of the UnitedStates is 1. A dynamometer for determining the power transmitted by arotating shaft, comprising two members attached to said shaft at adefinite distance apart, a mirror mounted on one of said members, andmeans whereby relative angular motion of the two members due to torsionof theshaft imparts It may here angular motion to the mirror.

2. A dynamometer for determining the power transmitted by a rotatingshaft, comprising two members attached to said shaft at a definitedistance apart, a mirror mounted on one of said members, means wherebyrelative an ular motion of the two members due to torsion of the shaftimparts angular motion to the mirror, and means for opticallydetermining the extent of the aforesaid angular motion of the mirror.

3. A dynamometer for determining the power transmitted by a rotatingshaft, comprising two members attached to said shaft at a definitedistance a art, a spindle mount-k ed on one of said mem rs, a mirrorcarried by said spindle, a laterally projecting arm thereon, and anactuatin plate engaging with said arm and carrie gy the other member.

4. A dynamometer for determining the power transmitted by a rotatingshaft, comprising two members attached to said shaft atv a definitedistance apart, a spindle mounted on one of said members, a mirrorcarried by said spindle, a laterally projecting arm thereon, anactuating plate en aging with said arm and carried by the oter member,an adjustably situated sourceV of light directing a beam onto saidmirror, and means whereby the deviation imparted to said beam, owing ltotorslon of the shaft, can be seen and determined 1n amount.

5. A dynamometer for determining the power transmitted by a rotatingshaft, comprising two members attached to said shaft at a definitedistance apart, a mirror mounted on one of said members, means wherebyrelative angular motion of the two membersv due to torsion of the shaftimparts angular motion to the mirror, and f, means whereby other smallangular motions between the two members are not communicated to the mir'ror, and means for optically determining the extent of the aforesaidangular motion of the mirror due to torsion of the shaft.

In testimony whereof we aiiix our signatures in presence of twowitnesses.

BERTRAM HOPKINSON. n LEONARD GODFREY PINNEY THRING.

Vitnesses T. A. G. CoeKERToN, E. FREEMAN.

